This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application entitled DEVICE AND METHOD FOR CONTROLLING POWER OF ORTHOGONAL CHANNEL AND QUASI-ORTHOGONAL CHANNEL IN CDMA COMMUNICATION SYSTEM earlier filed in the Korean Industrial Property Office on Mar. 26, 1998, and there duly assigned Serial No. 98-10616.
1. Field of the Invention
The present invention relates to a power control device and method for a CDMA communication system, and in particular, to a device and method for controlling powers of channels using orthogonal codes and quasi-orthogonal codes for spreading codes.
2. Description of the Related Art
In a forward link of an IS-95 code division multiple access (CDMA) communication system, a single family of orthogonal codes are used for the respective channels as spreading codes for channel separation. A mobile station despreads received signals using orthogonal codes (or Walsh codes) assigned by a base station. Although signals received at the mobile station may include signals that the base station has directed to other mobile stations, the mobile station can effectively disregard the signals directed to other mobile stations by despreading the received signals using a unique orthogonal code assigned to itself. In addition, for channel separation, different orthogonal codes are assigned to the respective channels, so that there is almost no receiving strength difference among the channels.
However, in the case where quasi-orthogonal codes, are used for the CDMA forward link channelization spreading code, the channels which are spread with different kinds of spreading codes (i.e., the quasi-orthogonal code) may be assigned to the forward link spreading code in the base station. For example, the orthogonal and quasi-orthogonal codes may refer to a different type of the orthogonal codes and non-orthogonal codes besides the quasi-orthogonal codes. For more details about the quasi-orthogonal codes, see Korean patent application No. 46402/1997 filed by the applicant of the invention. In the present invention, quasi-orthogonal codes may be generated by other means in addition to that described by the embodiments of the present invention. That is, the quasi-orthogonal codes are codes satisfying three conditions: 1) a condition of Walsh codes and a full length correlation; 2) Walsh code and partial correlation; and 3) full length correlation between quasi-orthogonal codes. In the case where an orthogonal code is not received above a constant level in the base station, at least one channel among channels assigning to the mobile station assigns a reference ortho-code, and other channels assign the ortho-code, thereby to distinguish the channels.
In case where the orthogonal code does not rise above a predetermined threshold in the base station, at least one channel among those channels assigned to the mobile station is assigned a reference ortho-code, and the other channels are assigned ortho-codes, to distinguish the respective channels.
The mobile station then acquires channel information transmitted from the base station by despreading received signals with an orthogonal code assigned to itself and also acquires channel information by despreading the received signals with a quasi-orthogonal code assigned to itself.
The orthogonal codes which are assigned to the mobile station and used in despreading have a high orthogonality with one another, so that there is virtually no interference from other forward channels. By contrast, the quasi-orthogonal codes which are assigned to the mobile station, and used in despreading have a relatively lower orthogonality with those assigned to other forward channels. Accordingly, interference among the channels despread with the quasi-orthogonal codes is higher than that among the channels despread with the orthogonal codes. The mobile station measures a signal-to-interference ratio (SIR) and requests the base station to increase the signal power when the measured channel performance is low. Despreading with the orthogonal code channel at the mobile station results in a higher SIR, whereas despreading with the quasi-orthogonal code channel results in a lower SIR. Therefore, a problem may arise if the power control is generally performed on all channels on the basis of the SIR of a specific code channel. Accordingly, there is a need for an improved power control method whenever a base station spreads signals using orthogonal and quasi-orthogonal codes.
According to the present invention, there is provided an apparatus and method for controlling the power of channels using orthogonal spreading codes and quasi-orthogonal spreading codes.
It is therefore an object of the present invention to provide a device and method for separately controlling the transmitting the power of channels in a CDMA communication system using orthogonal and quasi-orthogonal codes.
It is another object of the present invention to provide a device and method for controlling transmitting the power of channels by separating channel signals spread with orthogonal codes and quasi-orthogonal codes and measuring signal-to-interference ratios (SIRs) of the respective coded channel signals in a CDMA communication system.
In one aspect of the present invention a device and method is provided for controlling transmitting the power of channels spread with orthogonal codes and quasi-orthogonal codes spread with a single power control command in a CDMA communication system.
In another aspect of the present invention a device and method is provided for controlling a transmitting power ratio between channels in a CDMA communication system using orthogonal and quasi-orthogonal codes, in which a base station transmits a message to a mobile station according to a pre-set power ratio and determines whether the mobile station responds to the transmitted message within a predefined time.
In another aspect of the present invention a device and method is provided for controlling a transmitting power ratio between channels in a CDMA communication system using orthogonal and quasi-orthogonal codes, in which a mobile station sends a response request message to a base station, and the base station sends an acknowledge message and determines whether the same message is repeatedly received from the mobile station, to control the power ratio between the channels.
In another aspect of the present invention to provide a device and method for controlling a power ratio between channels according to the errors generated while decoding a channel spread with a quasi-orthogonal code at a mobile station.